Optical waveguide member and optical module

ABSTRACT

The present invention has an object of enhancing the tolerance of setup positioning error of an optical multiplexer/demultiplexer which uses a multi-mode optical waveguide. For this sake, the invention is designed to couple the multi-mode optical waveguide with a single-mode optical waveguide directly. In another configuration of this invention, there is provided between both optical waveguides a single-mode optical waveguide having its length set to be approximately equal to zero, or equal or approximately equal to the period of interference between the 0th-order mode and a radiative higher-order mode of the single-mode optical waveguide.

TECHNICAL FIELD

The present invention relates to an optical waveguide member and anoptical module, and particularly to an optical multiplexer/demultiplexerand an optical module using the same.

BACKGROUND ART

Attention is paid to the wavelength division multiplexing (WDM) systemfrom the viewpoint of enhanced speed and capacity of opticalcommunication. The optical multiplexer/demultiplexer is indispensabledevice for the WDM system. The devices in the type used by being coupledwith a single-mode fiber are particularly crucial. The reason is thatusing a single-mode fiber can transmit optical signals at lessdeterioration of signal waveform.

As a conventional device, there is known an optical demultiplexerdescribed in publication: Applied Physics Letter, Vol. 61, No. 15, pp.1754–1756, published in 1992, for example.

FIG. 13 is a plan view of a typical example of the device. This deviceis made up of a single-mode waveguide 10 of one core, a multi-modewaveguide 2, and a single-mode waveguide array 3 of four cores, with allparts being coupled to series in the optical axis direction on asubstrate 1. When the device is used as demultiplexer, a single-modefiber 4 is coupled to the 1-core side and a light is put in to thesingle-mode waveguide 10. The light excites in multiple modes atincidence to the multi-mode waveguide 2 and branches to four ways due tothe interference among the modes, and then is conducted from thesingle-mode waveguide array 3 to 4-core single-mode fibers 4′.

The above-said conventional device has its single-mode waveguide 10located between the 1-core single-mode fiber 4 and the multi-modewaveguide 2, so that the light is incident to the center of themulti-mode waveguide 2. In this case, however, if there is misalignmentbetween the single-mode fiber 4 and the device on its 1-core side, aradiative light 14 of a higher-order mode excites in the single-modewaveguide 10. This higher-order mode light 14 interferes with the0th-order mode light 13. Due to the fluctuation of light distributionduring the propagation, even a small misalignment can cause the incidentlight going into the multi-mode waveguide 2 to deviate greatly inposition and direction from the center axis. FIG. 14 shows the relationin this event among the center axis 11 of the single-mode fiber 4, thecenter axis 12 of the single-mode waveguide 10, and the peak positions15 of the light intensity. Other portions of this figure are referred toby the same symbols as those of FIG. 13. There arises a significantinequality in light output among the channels. Therefore, highpositioning accuracy is required in setting up the device, and it isdifficult to lower the setup cost based on a simple passive alignmentmethod.

In view of the foregoing situation, it is an object of the presentinvention to provide an optical multiplexer/demultiplexer which haslarge tolerance of setup positioning error against the single-mode fiberand allows modular setup based on a low cost simple passive alignmentmethod.

Japanese Patent Laid-Open No.H10 (1998)-48458 describes an exampledirectly coupling of a multi-mode fiber to a multi-mode waveguide.However, this patent publication pertains solely to a technique of theuse of a multi-mode fiber.

DISCLOSURE OF THE INVENTION

A representative from of this invention is characterized by couplingoptically a multi-mode waveguide 2 and a 1-core single-mode fiber 4directly. The inventive optical waveguide member can be used either asoptical multiplexer or as optical demultiplexer. Depending on as towhether the optical waveguide member is used as optical multiplexer orused as optical demultiplexer, it is different in light input direction.The inventive optical waveguide member can have the attachment of anoptical device or optical elements at the input port or output portdepending on the purpose.

The invention resides in an optical waveguide member which ischaracterized by comprising, at least, a multi-mode optical waveguideand a plurality of single-mode optical waveguides which are coupledoptically to a first end face of the multi-mode optical waveguide, themulti-mode optical waveguide being adapted to couple optically on itssecond end face, which is opposite to the first end face, with asingle-mode fiber.

It is significant for the inventive device to have the setting of thelength of the single-mode optical waveguide which is coupled opticallyto the second end face of the multi-mode optical waveguide. The mannerof setting will be explained in detail later.

For the explanation of the principle of this invention, the relationbetween the length of 1-core single-mode waveguide and the insertionloss will be exemplified. FIG. 15 shows a calculation result of therelation between the length L_(IN) of 1-core single-mode waveguide andthe insertion loss of the case of misalignment of 1.0 μm in thehorizontal direction existing between the optical demultiplexer having asingle-mode waveguide and the 1-core single-mode fiber 4. Thecalculation is based on the beam propagation method. The insertion losssignifies the optical loss attributable to the insertion of theinventive optical waveguide member on the light path.

FIG. 15 also shows the characteristics inherent to the typical devicestructure of this invention, i.e., L_(IN)=0. Channels CH1 through CH4represent the characteristics of the 4-core single-mode opticalwaveguide. In this example, the outer single-mode optical waveguides CH1and CH4 are larger in insertion loss relative to other waveguides CH2and CH3. On the other hand, the characteristic graph reveals that theinequality of insertion loss among the channels becomes very small atcertain intervals of length. The inventive device adopts a structurewithout a 1-core single-mode optical waveguide or a structure with a1-core single-mode optical waveguide having such a waveguide length thatthe inequality of characteristics among the channels is very small. Itis appreciated that the inventive device structure can reduce theinequality of insertion loss among the channels, which is attributableto the positioning error in the horizontal direction between the opticaldemultiplexer having a single-mode waveguide and the 1-core single-modefiber 4, by about 5 dB from the worst-case value of the conventionaldevice. It is most desirable to couple optically the multi-modewaveguide 2 and the 1-core single-mode fiber 4 directly, as mentionedpreviously, which should be also affirmative from the viewpoints ofperformance and manufacturing.

The following explains the period of intervals at which the inequalityof optical waveguide characteristics is minimal and various forms ofthis invention.

As shown in FIG. 15, there are lengths L_(IN) in a period of intervalsof 200–250 μm at which the inequality of insertion loss among thechannels virtually vanishes, besides the case where the length L_(IN) of1-core single-mode waveguide is zero. This period is the beat length ofinterference between the 0th-order mode 13 and radiative higher-ordermode 14 as shown in FIG. 14, and it is equal to a value which is thevalue of π divided by the difference of propagation constants of bothmodes.

Accordingly, the inventive device may have its length L_(IN) set to bean n-fold (n=0, 1, 2, . . . ) period of interference. This design schemeof an optical multiplexer/demultiplexer of the multi-mode interference(MMI) type implies the comprehension of the radiation mode in contrastto the conventional scheme which merely considers the waveguide mode.

As a result of interference, the insertion loss among the channelsvaries with the length L_(IN) periodically in a fashion of trigonometricfunction. On this account, even if the value of L_(IN) is differentslightly from an n-fold value of interference period, the inequality ofinsertion loss among the channels can be minimized, whereby the intendedcharacteristic can be attained.

Specifically, even with L_(IN) set within ⅕ of interference period, theobject of this invention can be achieved adequately. In other words,L_(IN) can be said virtually to be within ±40 μm. According to thiscondition, the device is sufficiently applicable to modules which areintended for the 10 Gb Ethernet for example.

Furthermore, L_(IN) can be set within a range from an n−⅕ fold (n=0,1,2,. . . ) interference period to an n+⅕ fold interference period. In otherwords, L_(IN) can range within from ±40 μm to an n-fold (n=0,1,2, . . .) value of interference period. Even in this case, the inequality ofinsertion loss among the channels can be reduced by about 3 dB from theworst-case value of the conventional device.

More preferably, L_(IN) is set in a range within 1/10 of theinterference period. In other words, more preferably, L_(IN) is setwithin 20 μm.

Alternatively, the same effect can be attained by setting L_(IN) in arange from an n− 1/10 fold (n=0,1,2, . . . ) interference period to ann+ 1/10 fold interference period. In other words, more preferably,L_(IN) is made to range from an n-fold (n=0,1,2, . . . ) value ofinterference period to ±20 μm. In this case, the inequality of insertionloss among the channels can be expected to decrease by nearly 4 dBrelative to the worst-case value of the conventional device.

Although the foregoing explanation is of the odd-numbered order of ahigher mode 14 which interferes with the 0th-order mode 13, theinterference period of the case of an even-numbered order is obtained asa value which is the value of 2π divided by the difference ofpropagation constants between the 0th-order mode 13 and a higher-ordermode 14.

In practicing this invention, it is optically desirable to have thecoincidence between the center axis of the multi-mode waveguide and thecenter axis of the single-mode waveguide which is coupled optically tothe second end face of the multi-mode waveguide. This configuration iscommon among the variant forms of this invention.

Although the foregoing explanation deals with the optical demultiplexerto exemplify the inventive optical waveguide member, the opticalmultiplexer and demultiplexer have the same principle of operation, withonly difference being their opposite light propagation directions.Therefore, the inventive device when used as an optical multiplexer cansecure a large tolerance of setup positioning error as in the case ofthe optical demultiplexer.

This invention is significant in terms of enabling the enhancement ofthe tolerance of setup positioning error of optical demultiplexer basedon direct coupling of the single-mode fiber to the multi-mode waveguide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a first embodiment of this invention;

FIG. 2 is a plan view showing a second embodiment of this invention;

FIG. 3 is a perspective view showing one configuration the secondembodiment of this invention;

FIGS. 4A to 4C are partial cross-sectional diagrams showing thefabrication steps of the polymer optical waveguide section of the secondembodiment of this invention;

FIG. 5 is a plan view showing a third embodiment of this invention;

FIG. 6 is a plan view showing a fourth embodiment of this invention;

FIG. 7 is a plan view showing a fifth embodiment of this invention;

FIG. 8 is a plan view showing a sixth embodiment of this invention;

FIG. 9 is a plan view showing a seventh embodiment of this invention;

FIG. 10 is a plan view showing an eighth embodiment of this invention;

FIG. 11 is a plan view showing a ninth embodiment of this invention;

FIG. 12 is a plan view showing a tenth embodiment of this invention;

FIG. 13 is a plan view showing a conventional example;

FIG. 14 is a plan view showing the propagation of light in theconventional arrangement; and

FIG. 15 is a graph showing an example of the relation between the lengthof single-mode waveguide in the 1-core side and the insertion loss.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

The embodiments of this invention will be described.

FIG. 1 shows the first embodiment of this invention. The figure is abrief top view of the device. The device of this embodiment can be usedas optical multiplexer and also as optical demultiplexer. In thisembodiment, a multi-mode waveguide 2 and a 4-core single-mode waveguidearray 3 are coupled optically on a substrate 1. The multi-mode waveguide2 has its another end face, which does not couple to the single-modewaveguide array 3, coupled optically with a single-mode fiber 4directly. On this account, this structure can minimize the inequality ofinsertion loss among the channels even in the presence of a positioningerror between the multi-mode waveguide 2 and the single-mode fiber 4 asdescribed previously. It is significant, as shown in this embodiment, tocouple the single-mode fiber directly to the multi-mode waveguide.

FIG. 2 shows the second embodiment of this invention. The figure is abrief top view of the device. This embodiment is an example of opticaltransmission module. Also in this embodiment, as in the firstembodiment, a multi-mode waveguide 2 and a 4-core single-mode waveguidearray 3 are coupled optically on a substrate 1. The multi-mode waveguide2 has its another end face, which does not couple with the single-modewaveguide array 3, coupled optically with a single-mode fiber 4directly. This module has a V-groove 6 formed in the substrate 1, whichis identical to that of the device of the first embodiment, therebypositioning and fixing the single-mode fiber 4 on the substrate 1. TheV-groove 6 is formed along the axial direction of the optical fiber. Thesubstrate 1 is, in general, a silicon substrate for example. TheV-groove, i.e., a groove with a V-shaped cross section, is formedprecisely by anisotropic etching of crystalline silicon. The groovestructure of crystalline silicon formed by anisotropic etching isusually called “V-groove”. In practice, however, there can be U shapesbesides the exact V shape and variations of these shapes. The term“V-groove” or “V-shape groove” used in this document of patentapplication comprehends all of these shapes of groove. Substratesthemselves having the V-shape groove structure are known in the art, anddetailed explanation thereof is omitted. There can be other means forthis purpose obviously.

In addition, the inventive device has the formation of a dicing groove 7for rectifying the end face of the V-groove 6. There are foursemiconductor lasers 5 of the distributed feedback (DFB) type havingdifferent oscillation wavelengths mounted on the substrate 1, which arecoupled optically with the single-mode waveguide array 3. The DFBsemiconductor lasers 5 are driven by being connected to a transmissionLSI 40 through wiring lines 41. This module is capable of multiplexinglights of different wavelengths generated by the four DFB semiconductorlasers 5 and conducting to the single-mode fiber 4 at a small loss and asmall inequality of loss among the channels. The module is alsooperative as a reception module by replacing the DFB semiconductorlasers with photodiodes of the waveguide type and replacing thetransmission LSI with a reception LSI. The module has large tolerance ofsetup positioning error in regard to the inequality of insertion lossamong the channels. It is significant also in this embodiment to couplethe single-mode fiber 4 directly to the multi-mode waveguide 2 asdescribed previously.

FIG. 3 shows by perspective view an example of fabrication of thepreceding second embodiment by use of a Si substrate and a polymerwaveguide. The portion of LSI is not shown in the figure. In thismodule, the multi-mode waveguide 2 and single-mode waveguide array 3shown in FIG. 2 are formed of a lower clad layer made of polymer (willbe termed “lower polymer clad layer”) 22, a core layer made of polymer(will be termed “polymer core layer”) 23, and an upper clad layer madeof polymer (will be termed “upper polymer clad layer”) 24. This polymerwaveguide is formed on a Si substrate 20 which is coated on its surfacewith a silicon dioxide film (will be termed “SiO₂ film”) 21. The rest isidentical to the second embodiment. Specifically, the optical fiber 4 isfitted by being positioned on the V-groove 6. A dicing groove 7 isformed to rectify the end face of the V-groove 6. Four-core single-modewaveguides 231,232,233 and 234 are connected to DFB semiconductor lasers51,52,53 and 54, respectively.

The module fabricated as described above attained the tolerancecharacteristic of positioning error of 1.0 μm or more against thesingle-mode fiber 4. Namely, the inequality among the channels is 0.5 dBor less. This example is for an operational wavelength band of 1.3 m.

FIG. 4 shows the fabrication process of the optical waveguide section ofthe module described above. The usual fabrication process suffices tomake it. FIGS. 4A to 4C are cross-sectional diagrams of the principalportion of the waveguide, showing the sequential steps of fabricationprocess.

For fabricating the optical waveguide, a Si substrate 20 on which anSiO₂ film 21 is formed is prepared, and a lower polymer clad layer 22and polymer core layer 23 are formed on the SiO₂ film 21: (shown in FIG.4A). Next, the polymer core layer 23 is etched to leave portions incorrespondence to the 4-core single-mode waveguides 231,232,233 and 234:(shown in FIG. 4B) On the resulting substrate, an upper polymer cladlayer 24 is formed, and a polymer optical waveguide is completed:(shownin FIG. 4C). Typical polymer materials used in fabrication includepolyimide, polysiloxane, epoxy resin, acrylate resin, and fluorinatedpolymers of these resins.

The V-groove 6 of the silicon substrate 20 of the module can be formedby the anisotropic wet etching process which uses KOH solution forexample.

In regard to the property of module for specific applications, thedimensions of optical waveguide core are about 6.5 μm by 6.5 μm, therefractivity of clad is about 1.525, the difference of refractivitybetween the clad and the core is around 0.4%–0.5%, for example. Thewavelength band used by this optical module is about from 1250 nm to1375 nm for example. Generally, four center wavelengths of 1257.7 nm,1300.2 nm, 1324.7 nm and 1349.2 nm are used for the 10 GbE-WWDM.

Although the foregoing explanation is of the case of use of DFB-typesemiconductor lasers or waveguide-type photodiodes, semiconductor lasersor photodiodes of other types or other optical elements can be useddepending on the requirement of individual optical systems.

FIG. 5 shows the third embodiment of this invention. This embodiment isan example which is derived from the second embodiment, with single-modefibers 4, in place of the DFB semiconductor lasers 5, being coupledoptically to the single-mode waveguide array 3. The rest is identical tothe preceding embodiments, and detailed explanation is omitted. Thisembodiment can be used as optical multiplexer or also as opticaldemultiplexer. Moreover, in this embodiment, all or part of the opticalfibers which are coupled optically to the single-mode waveguide array 3may be replaced with multi-mode fibers. In this case, this embodimentcan be operated as optical demultiplexer.

FIG. 6 shows the fourth embodiment of this invention. The device of thisembodiment is an example in which the substrate of optical module isformed of multiple parts. Specifically, this example employs a secondsubstrate 8 which is separate from the substrate 1 on which themulti-mode waveguide 2 and single-mode waveguide array 3 are formed.Formed on the second substrate 8 is a second single-mode waveguide array9. The rest is identical to the embodiment of FIG. 5.

This embodiment is an example which is derived from the secondembodiment, with the second single-mode waveguide array 9, in place ofthe DFB semiconductor lasers 5, being coupled optically with thesingle-mode waveguide array 3. This embodiment can also be used asoptical multiplexer and also as optical demultiplexer. In case thedevice of this embodiment is used as optical demultiplexer, a multi-modewaveguide array or a waveguide array made up of multi-mode waveguidesand single-mode waveguides can be used in place of the single-modewaveguide array 9.

FIG. 7 shows the fifth embodiment of this invention. This embodiment isan example of optical multiplexer. This embodiment is derived from theoptical module of the second embodiment, with the single-mode fiber 4having its end face, which does not couple with the multi-mode waveguide2, coupled to a multi-mode fiber 30. This arrangement enables the singlemode from the single-mode fiber 4 to be incident to the center of themulti-mode fiber 30, whereby the waveguide mode can be rousedefficiently in the multi-mode fiber 30. The rest is identical to theembodiment of FIG. 2. As shown in this embodiment, this invention can beused effectively for optical transmission through a multi-mode fiber.

The inventive device can have an arbitrary number of single-modewaveguides of the single-mode waveguide array 3, instead of beingconfined to four waveguides which have been shown in the figures for theexplanation of the preceding embodiments. FIG. 8 shows, as the sixthembodiment, an example of module having seven single-mode waveguides.

The inventive device may be provided, between the multi-mode waveguide 2and the single-mode fiber 4, with a single-mode waveguide 10 having afinite length around 0 μm. FIG. 9 shows, as the seventh embodiment, anoptical multiplexer/demultiplexer having such a structure. Thisembodiment can also have large tolerance of setup positioning error asexplained above. The above-mentioned “a finite length around 0 μm” forthe length of the single-mode waveguide 10 is more specifically asexplained in detail in the section entitled Disclosure of the Invention.The allowable range of the length has been explained in connection withFIG. 15.

The following configurations of optical waveguide member are practicallyuseful. In one case, the single-mode waveguide in optical coupling withthe second end face of the multi-mode waveguide has a center value ofthe allowable range of length set equal to a value which is the value ofπ divided by the difference of propagation constants between the0th-order eigen mode and the radiative first-order mode of thesingle-mode waveguide. In another case, the single-mode waveguide inoptical coupling with the second end face of the multi-mode waveguidehas a center value of the allowable range of length set equal to a valuewhich is the value of 2π divided by the difference of propagationconstants between the 0th-order eigenmode and the radiative second-ordermode of the single-mode waveguide. Optical modules using these opticalwaveguide members are useful.

It is desirable practically for these optical waveguide members to beconfigured such that the center axis of the multi-mode waveguide iscoincident with the center axis of the single-mode waveguide which iscoupled optically to the second end face of the multi-mode waveguide.

FIG. 10 shows the eighth embodiment of this invention. This embodimentis an example of transmission module or reception module based on thedevice of the previous seventh embodiment. With the single-modewaveguide array 3 being coupled with single-mode fibers or single-modewaveguides in place of optical elements, the module can be operative asoptical multiplexer/demultiplexer.

The inventive device may be provided, between the multi-mode waveguide 2and the single-mode fiber 4, with a single-mode waveguide 10 having itslength set to be equal or approximately equal to the period ofinterference between the 0th-order mode and a radiative higher-ordermode. FIG. 11 shows the ninth embodiment having this structure. Thiscase also can have large tolerance of setup positioning error asexplained above. The specific length of the single-mode waveguide 10 isas explained in detail in the section entitled Disclosure of theInvention.

FIG. 12 shows the tenth embodiment of this invention. This embodiment isan example of transmission module or reception module based on thedevice of the previous ninth embodiment.

With the single-mode waveguide array 3 being coupled with single-modefibers or single-mode waveguides in place of optical elements, themodule can be operative as optical multiplexer/demultiplexer.

This invention is effective regardless of the materials of thesubstrate, waveguides and other constituents, and is not confined to thecases explained in the foregoing embodiments. In addition, thisinvention is effective regardless of the positioning and fixing mannersof the single-mode fiber, optical elements, waveguides, and otherconstituents, and is not confined to the cases explained in theforegoing embodiments.

The following itemizes various cases of the length of the single-modeoptical waveguide which is coupled optically to the second end face ofthe multi-mode waveguide. Cases represented solely in terms of specificnumerals, such as 20 μm or less, or 40 μm or less, are excluded.

-   (1) In an optical waveguide member including a multi-mode optical    waveguide, a plurality of first single-mode optical waveguides which    are coupled optically to a first end face of the multi-mode optical    waveguide, and at least one second single-mode waveguide which is    coupled optically to a second end face, which is opposite to the    first end face, of the multi-mode optical waveguide, the second    single-mode optical waveguide has a length which is at least in any    of a range (positive number) from n−⅕ fold to n+⅕ fold values (where    n=0,1,2, . . . ) of the period of interference between the 0th-order    eigenmode and a radiative higher-order mode of the second    single-mode waveguide, a range (positive number) from n−⅕ fold to    n+⅕ fold values (where n=0,1,2, . . . ) of a value which is the    value of π divided by the difference of propagation constants    between the 0th-order eigen mode and a radiative higher-order mode    of the second single-mode waveguide, and a range (positive number)    from n−⅕ fold to n+⅕ fold values (where n=0, 1,2, . . . ) of a value    which is the value of 2π divided by the difference of propagation    constants between the 0th-order eigen mode and a radiative    higher-order mode of the second single-mode waveguide.-   (2) In an optical waveguide member set forth in item (1), the    above-said single-mode waveguide which is coupled optically to the    second end face of the multi-mode waveguide has a length which    ranges (positive number) from n− 1/10 fold to n+ 1/10 fold values    (where n=0, 1, 2, . . . ) of the period of interference between the    0th-order eigen mode and a radiative higher-order mode of the    above-said single-mode waveguide.-   (3) In an optical waveguide member including, at least, a multi-mode    optical waveguide, a plurality of single-mode optical waveguides    which are coupled optically to a first end face of the multi-mode    optical waveguide, a single-mode optical waveguide which is coupled    optically to a second end face, which is opposite to the first end    face, of the multi-mode optical waveguide, and a single-mode fiber    which is coupled optically to a second end face, which is opposite    to a first end face coupled to the multi-mode optical waveguide, of    the single-mode optical waveguide, the above-said single-mode    optical waveguide has a length which ranges (positive number) from    an n-fold value (where n=0, 1, 2, . . . ) of the period of    interference between the 0th-order eigen mode and a radiative    higher-order mode of the above-said single-mode waveguide to ±40 μm.-   (4) In an optical waveguide member set forth in item (4) the    above-said single-mode waveguide which is coupled optically to the    second end face of the multi-mode waveguide has a length which    ranges (positive number) from an n-fold value (where n=0,1,2, . . .    ) of the period of interference between the 0th-order eigen mode and    a radiative higher-order mode of the above-said single-mode    waveguide to ±20 μm.-   (5) In an optical waveguide member including, at least, a multi-mode    optical waveguide, a plurality of single-mode optical waveguides    which are coupled optically to a first end face of the multi-mode    optical waveguide, a single-mode waveguide which is coupled    optically to a second end face, which is opposite to the first end    face, of the multi-mode optical waveguide, and a single-mode fiber    which is coupled optically to a second end face, which is opposite    to a first end face coupled to the multi-mode optical waveguide, of    the single-mode optical waveguide, the above-said single-mode    optical waveguide has a length which ranges (positive number) from    n−⅕ fold to n+⅕ fold values (where n=0,1,2, . . . ) of a value which    is the value of π divided by the difference of propagation constants    between the 0th-order eigenmode and a radiative higher-order mode of    the above-said single-mode waveguide.-   (6) In an optical waveguide member set forth in item (5) the    above-said single-mode waveguide which is coupled optically to the    second end face of the multi-mode waveguide has a length which    ranges (positive number) from n− 1/10 fold to n+ 1/10 fold values    (where n=0,1,2, . . . ) of a value which is the value of π divided    by the difference of propagation constants between the 0th-order    eigenmode and a radiative higher-order mode of the above-said    single-mode waveguide.-   (7) In an optical waveguide member including, at least, a multi-mode    optical waveguide, a plurality of single-mode optical waveguides    which are coupled optically to a first end face of the multi-mode    optical waveguide, and a second single-mode waveguide which is    coupled optically to a second end face, which is opposite to the    first end face, of the multi-mode optical waveguide, the above-said    single-mode optical waveguide is adapted to couple optically on its    second end face, which is opposite to the first end face in coupling    with the multi-mode optical waveguide, with a single-mode fiber, and    the above-said single-mode optical waveguide has a length which    ranges (positive number) from a value which is the value of π    divided by the difference of propagation constants between the    0th-order eigenmode and a radiative higher-order mode of the    above-said single-mode waveguide to ±40 μm.-   (8) In an optical waveguide member, the above-said single-mode    waveguide which is coupled optically to the second end face of the    multi-mode waveguide has a length which ranges (positive number)    from a value which is the value of π divided by the difference of    propagation constants between the 0th-order eigenmode and a    radiative higher-order mode of the above-said single-mode waveguide    to ±20 μm.-   (9) In an optical waveguide member including, at least, a multi-mode    optical waveguide, a plurality of single-mode optical waveguides    which are coupled optically to a first end face of the multi-mode    optical waveguide, and a single-mode waveguide which is coupled    optically to a second end face, which is opposite to the first end    face, of the multi-mode optical waveguide, the above-said    single-mode optical waveguide is adapted to couple optically on its    second end face, which is opposite to the first end face in coupling    with the multi-mode optical waveguide, with a single-mode fiber, and    the above-said single-mode optical waveguide has a length which    ranges (positive number) from n−⅕ fold to n+⅕ fold values (where    n=0, 1,2, . . . ) of a value which is the value of 2π divided by the    difference of propagation constants between the 0th-order eigenmode    and a radiative higher-order mode of the above-said single-mode    waveguide.-   (10) In an optical waveguide member, the above-said single-mode    waveguide which is coupled optically to the second end face of the    multi-mode waveguide has a length which ranges (positive number)    from n− 1/10 fold to n+ 1/10 fold values (where n=0,1,2, . . . ) of    a value which is the value of 2π divided by the propagation    constants between the 0th-order eigenmode and a radiative    higher-order mode of the above-said single-mode waveguide.-   (11) In an optical waveguide member including, at least, a    multi-mode optical waveguide, a plurality of single-mode optical    waveguides which are coupled optically to a first end face of the    multi-mode optical waveguide, and a single-mode waveguide which is    coupled optically to a second end face, which is opposite to the    first end face, of the multi-mode optical waveguide, the above-said    single-mode optical waveguide is adapted to couple optically on its    second end face, which is opposite to the first end face in coupling    with the multi-mode optical waveguide, with a single-mode fiber, and    the above-said single-mode optical waveguide has a length which    ranges (positive number) from a value which is the value of 2π    divided by the difference of propagation constants between the    0th-order eigenmode and a radiative higher-order mode of the    above-said single-mode waveguide to ±40 μm.-   (12) In an optical waveguide member set forth in item (11) the    above-said single-mode waveguide which is coupled optically to the    second end of the multi-mode waveguide has a length which ranges    (positive number) from a value which is the value of 2π divided by    the difference of propagation constants between the 0th-order    eigenmode and a radiative higher-order mode of the above-said    single-mode waveguide to ±20 μm.

The following itemizes practical configurations of the inventive opticalwaveguide member.

Firstly, the inventive optical waveguide member is characterized byhaving at least one of its multi-mode waveguide and single-modewaveguide formed of a material of polymer.

Secondly, the inventive optical waveguide member is characterized byhaving at least one of its multi-mode waveguide and single-modewaveguide formed on a silicon substrate.

Thirdly, the inventive optical waveguide member is characterized byhaving its single-mode optical waveguide coupled optically on one endface thereof, which is different from another end face in coupling withthe multi-mode waveguide, with a single-mode fiber.

Fourthly, the single-mode fiber is fixed by means of a V-shape groove ora groove of other cross-sectional shape formed in the substrate which isshared with the multi-mode waveguide or single-mode waveguides.

Fifthly, the inventive optical waveguide member is characterized in thatthe single-mode fiber is coupled optically on its end face, which doesnot couple optically with neither the single-mode waveguide nor themulti-mode waveguide, with a multi-mode fiber. It is desirable that thetechnical concept of the invention be applied to the third and fourthitems.

The following itemizes examples of optical module of this patentapplication.

A first configuration of optical module comprises at least one opticalmultiplexer or optical demultiplexer of this invention, and ischaracterized in that at least one of the single-mode waveguides, whichare coupled optically to a first end face of the multi-mode waveguideincluded in the optical multiplexer or optical demultiplexer, is coupledoptically on its end face, which does not couple optically with themulti-mode waveguide, with a single-mode fiber or multi-mode fiber.

A second configuration of optical module is derived from the firstconfiguration, and is characterized in that the single-mode fiber ormulti-mode fiber, which is coupled optically to the single-modewaveguide in optical coupling with the first end face of the multi-modewaveguide, is fixed by means of a V-shape groove or a groove of othercross-sectional shape formed in the substrate which is shared with themulti-mode waveguide or single-mode waveguides.

A third configuration of optical module is derived from the firstconfiguration, and is characterized in that semiconductor lasers of thedistribution feedback type or distribution reflection type havingdifferent oscillation wavelengths are coupled optically to thesingle-mode waveguides which are coupled optically to the first end faceof the multi-mode waveguide of the optical multiplexer.

A fourth configuration of optical module is derived from the firstconfiguration, and is characterized in that photodiodes of the waveguidetype are coupled optically to the single-mode waveguides which arecoupled optically to the first end face of the multi-mode waveguide ofthe optical demultiplexer.

Using the inventive optical waveguide members and elements enables thesetup of module based on the inexpensive passive alignment scheme,whereby a low-cost optical module can be accomplished.

According to the embodiments of this invention, there are providedoptical waveguide members, e.g., optical multiplexer/demultiplexer,having large tolerance of setup positioning error.

CAPABILITY OF INDUSTRIAL APPLICATION

This invention resides in an optical waveguide member which ischaracterized by including a multi-mode optical waveguide and aplurality of first single-mode optical waveguides which are coupledoptically to a first end face of the multi-mode optical waveguide, withthe multi-mode waveguide being adapted to couple optically on its secondend face, which is opposite to the first end face, with a single-modefiber, and the invention can provide optical waveguide members, e.g.,optical multiplexer/demultiplexer, having large tolerance of setuppositioning error.

1. An optical waveguide member comprising: a multi-mode optical waveguide which is surrounded on a core exterior thereof by a clad, and a plurality of first single-mode optical waveguides which are coupled optically to a first end face of said multi-mode optical waveguide, said multi-mode optical waveguide being a multi-mode optical waveguide having a multi-mode interference effect, which performs optical multiplexing and optical demultiplexing in accordance with the multi-mode interference effect, and which is structured to directly couple optically on a second end face thereof, which is opposite to the first end face, with a single-core single-mode fiber; wherein at a position contiguous to the second end face of said multi-mode optical waveguide, a groove structure for holding an optical fiber to be coupled optically to the second end face of said multi-mode optical waveguide is set.
 2. An optical waveguide member comprising: a multi-mode optical waveguide which is surrounded on a core exterior thereof by a clad, and a plurality of first single-mode optical waveguides which are coupled optically to a first end face of said multi-mode optical waveguide, said multi-mode optical waveguide being a multi-mode optical waveguide having a multi-mode interference effect, which performs optical multiplexing and optical demultiplexing in accordance with the multi-mode interference effect, and which is structured to directly couple optically on a second end face thereof, which is opposite to the first end face, with a single-core single-mode fiber; and at least, a single-core single-mode fiber which is directly coupled optically to the second end face, which is opposite to the first end face, of said multi-mode optical waveguide; and wherein at a position contiguous to the second end face of said multi-mode optical waveguide, a groove structure for holding an optical fiber to be coupled optically to the second end face of said multi-mode optical waveguide is set, including a single-mode fiber which is coupled optically to the second end face of said multi-mode optical waveguide, and having said single-mode fiber held by means of said groove structure.
 3. An optical waveguide member set forth in claim 1, wherein at least one of said multi-mode optical waveguide and said first single-mode optical waveguides is formed of a material of polymer resin.
 4. An optical waveguide member set forth in claim 2, wherein at least one of said multi-mode optical waveguide and said first single-mode optical waveguides is formed of a material of polymer resin.
 5. An optical waveguide member set forth in claim 1, wherein at least one of said multi-mode optical waveguide and said first single-mode optical waveguides is formed on a silicon substrate.
 6. An optical waveguide member set forth in claim 2, wherein at least one of said multi-mode optical waveguide and said first single-mode optical waveguides is formed on a silicon substrate.
 7. An optical waveguide member comprising: a multi-mode optical waveguide, said multi-mode optical waveguide performing optical multiplexing/demultiplexing by using multi-mode interference, a plurality of first single-mode optical waveguides which are coupled optically to a first end face of said multi-mode optical waveguide, and at least one second single-mode optical waveguide which is coupled optically to a second end face, which is opposite to the first end face, of said multi-mode optical waveguide, said second single-mode waveguide having a length of 40 μm or less.
 8. An optical waveguide member set forth in claim 7, wherein said at least one second single-mode optical waveguide has third and fourth end faces, the third end face of said second single-mode optical waveguide being coupled optically to the second end face of said multi-mode optical waveguide, said member including a single-mode fiber which is coupled optically to the fourth end face which is opposite to the third end face in coupling with said multi-mode optical waveguide.
 9. An optical waveguide member set forth in claim 7, wherein said at least one second single-mode optical waveguide has third and fourth end faces, the third end face of said second single-mode optical waveguide being coupled optically to the second end face of said multi-mode optical waveguide, said at least one second single-mode optical waveguide having a length of 20 μm or less.
 10. An optical waveguide member set forth in claim 9, wherein a single-mode fiber is coupled optically to said fourth end face of said at least one second single-mode optical waveguide.
 11. An optical waveguide member set forth in claim 7, wherein said at least one second single-mode optical waveguide has third and fourth end faces, said third end face of said second single-mode optical waveguide being coupled optically to the second end face of said multi-mode optical waveguide, and at a position contiguous to said fourth end face of said second single-mode optical waveguide, a groove structure for holding an optical fiber to be coupled optically to the fourth end face is set.
 12. An optical waveguide member set forth in claim 8, wherein at a position contiguous to said fourth end face of said second single-mode optical waveguide, a groove structure for holding an optical fiber to be coupled optically to the fourth end face is set, and having a single-mode fiber which is coupled optically to the fourth end face of said multi-mode optical waveguide, and said single-mode fiber is held by means of said groove structure.
 13. An optical waveguide member set forth in claim 9, wherein at a position contiguous to said fourth end face of said second single-mode optical waveguide, a groove structure for holding an optical fiber to be coupled optically to the fourth end face is set.
 14. An optical waveguide member set forth in claim 7, wherein at least one of said multi-mode optical waveguide and said first and second single-mode optical waveguides is formed of a material of polymer resin.
 15. An optical waveguide member set forth in claim 7, wherein at least one of said multi-mode optical waveguide and said first and second single-mode optical waveguides is formed on a silicon substrate.
 16. An optical waveguide member comprising: a multi-mode optical waveguide, a plurality of first single-mode optical waveguides which are coupled optically to a first end face of said multi-mode optical waveguide, and at least one second single-mode optical waveguide which is coupled optically to a second end face, which is opposite to the first end face, of said multi-mode optical waveguide, wherein said second single-mode waveguide has a length which is at least in any of a range (positive number) from n−1/5 fold to n+1/5 fold values (where n=0, 1, 2, . . . ) of a period of interference between a 0th-order eigenmode and a radiative higher-order mode of said second single-mode waveguide, a range (positive number) from n−1/5 fold to n+1/5 fold values (where n=0, 1, 2, . . . ) of a value which is the value of π divided by a difference of propagation constants between the 0th-order eigenmode and a radiative higher-order mode of said second single-mode waveguide, and a range (positive number) from n−1/5 fold to n+1/5 fold values (where n=0, 1, 2, . . . ) of a value which is the value of 2π divided by the difference of propagation constants between the 0th-order eigenmode and a radiative higher-order mode of said second single-mode waveguide.
 17. An optical waveguide member set forth in claim 16, wherein said at least one second single-mode optical waveguide has a third and fourth end faces, the third end face of said second single-mode optical waveguide being coupled optically to the second end face of said multi-mode optical waveguide, said optical waveguide member including a single-mode fiber which is coupled optically to the fourth end face, which is opposite to the second end face in coupling with said multi-mode optical waveguide, of said single-mode optical waveguide.
 18. An optical module comprising: at least one of the optical waveguide member set forth in claim 1, said at least one of the optical waveguide member having at least one of a plurality of first single-mode optical waveguides which are coupled optically to the first end face of the multi-mode optical waveguide included in said optical waveguide member, and at least one member selected from a group of an optical element, an optical waveguide, a single-mode fiber, a multi-mode fiber and a groove structure for holding an optical fiber, on one end face, which does not couple optically with said multi-mode optical waveguide, of at least one of a plurality of the first single-mode optical waveguides.
 19. An optical waveguide member comprising: a multi-mode optical waveguide, a plurality of first single-mode optical waveguides which are coupled optically to a first end face of said multi-mode optical waveguide, and at least one second single-mode optical waveguide which is coupled optically to a second end face, which is opposite to the first end face, of said multi-mode optical waveguide, wherein said second single-mode waveguide has a length which is in a range (positive number) from an n-fold value (where n=0, 1, 2, . . . ) of a period of interference between a 0th-order eigenmode and a radiative higher-order mode of the above-said single-mode waveguide to ±40 μm.
 20. An optical waveguide member comprising: a multi-mode optical waveguide, a plurality of first single-mode optical waveguides which are coupled optically to a first end face of said multi-mode optical waveguide, and at least one second single-mode optical waveguide which is coupled optically to a second end face, which is opposite to the first end face, of said multi-mode optical waveguide, wherein said second single-mode waveguide has a length which is in a range (positive number) from an n-fold value (where n=0, 1 , 2, . . . ) which is a value of π divided by a difference of propagation constants between a 0th-order eigenmode and a radiative higher-order mode of the above-said single-mode waveguide to ±40 μm, or in a range (positive number) from an n-fold value (where n=0,1,2, . . .) which is a value of 2π divided by a difference of propagation constants between the 0th-order eigenmode and a radiative higher-order mode of the above-said single-mode waveguide to ±40 μm. 